Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$136.54	11.760%	$152.5971	$152.60	$152.60	$152.60
Purchase #2	$145.64	7.375%	$156.381	$156.38	$156.40	$156.40
Purchase #3	$51.86	3.694%	$53.7757	$53.78	$53.80	$53.80
Purchase #4	$195.27	7.793%	$210.4874	$210.49	$210.50	$210.50
Purchase #5	$129.43	3.670%	$134.1801	$134.18	$134.20	$134.20
Purchase #6	$71.93	8.455%	$78.0117	$78.01	$78.00	$78.00
Purchase #7	$138.61	5.627%	$146.4096	$146.41	$146.40	$146.40
7 purchase totals =	$869.28		$931.8426	$931.85	$931.90	$931.90